1. Field of the Invention
The present invention relates to a bendable portion control device (bendable portion steering device) for manipulating and steering the steerable bendable portion of a flexible insertion portion of an endoscope.
2. Description of the Related Art
In typical endoscopes, the steerable bendable portion provided in the vicinity of the distal end of the insertion portion of the endoscope can be bent freely in any direction at any angle (i.e., the orientation of the tip of the distal end can be freely adjusted) by pulling and extending control wires from a control portion coupled to the proximal end of the insertion portion of the endoscope, and the control portion is provided thereon with a freely-rotatable control knob (bendable portion control knob) for manually pulling and extending the control wires from the proximal end side thereof.
If a control wire is accidentally snapped (broken) by being acted upon by an excessive tensile force, an extremely troublesome overhaul is required; moreover, the bendable portion remains bent, which may make it difficult to remove the insertion portion of the endoscope from a body cavity safely. To prevent this problem from occurring, an endoscope in which each control wire is provided at some midpoint therein with a reduced-strength portion which is weaker in strength than the control wire has been proposed. In this endoscope, the reduced-strength portion breaks upon an excessive tensile force acts on the control wire. This structure is disclosed in, e.g., Japanese unexamined patent publication 2003-339630.
On the other hand, in conventional endoscopes in which the control wires are pulled and extended by a motor(s), an endoscope which is provided between the motor and the proximal end of an associated control wire with a friction clutch which slips upon a load over a predetermined load being exerted so that the bendable portion may not push a parietal (somatic wall) excessively hard and so that an excessive load is not exerted on the motor is known in the art. This type of endoscope is disclosed in, e.g., Japanese examined utility-model publication S55-54481.
However, as disclosed in JUPP 2003-339630, even if the aforementioned reduced-strength portion that is weaker in strength than the control wire is installed at some midpoint therein, the reduced-strength portion breaks upon the bendable portion control knob being rotated with an excessive torque. Once the reduced-strength portion breaks, the broken part needs to be fixed, so that the endoscopic operation cannot continue to be performed at any rate.
As disclosed in JEUMP S55-54481, in the configuration in which the aforementioned friction clutch that slips upon a load over a predetermined load being exerted is provided, a cork disk serving as a frictional member needs to be sandwiched between two metal disks, and additionally, a disk spring (belleville spring) or the like for setting an appropriate frictional force needs to be provided to be overlaid on the metal disks having the cork disk therebetween. Due to this structure, even if the friction clutch can be installed in a portion of the endoscope which does not have to be directly manually operated like a motor drive mechanism, the bendable portion control knob increases in size to thereby deteriorate the operability of the endoscope if one intends to install the friction clutch into, e.g., the internal space of the bendable portion control knob that is manually operated to manipulate the bendable portion. This increase in size of the bendable portion control knob results in a serious loss in the operability of the endoscope.